radicals for the degradation of DPAH. The rate of photodegradation was demonstrated in terms of irradiation time, pH, catalyst loading, and initial concentration. On the other hand, voltammetry was used to evaluate the electrochemical behavior of SrMoO4. The overall reaction pathways of DPAH showed that the major contribution of the reaction is generation of radical cations (DPAH+). Therefore, we can determine the concentration of DPAH by measuring DPAH+. Differential pulse voltammetry is a suitable analytical tool to measure DPAH+, which determined the DPAH in the linear range 0.1–35µM and with a lowest detection limit of 30nM. One of the greatest challenges of this determination is the selectivity, because DPAH+ is highly reactive toward similar functionalities such as anions and cations. Therefore, we carefully investigated and discussed the selectivity in the presence of interfering compounds.